Underarm pain in boys may be caused by folliculitis, inflammation of the lymph nodes in the armpit, suppurative sweating and so on. 1. Folliculitis: it is mainly caused by bacteria, viruses and other pathogenic bacteria, when folliculitis occurs in the armpit, due to the stimulation of inflammation can appear red pimples, itching and pain. 2. Inflammation of axillary lymph nodes: it may be caused by bacterial infection. Due to the stimulation of inflammation, patients may have symptoms such as redness, swelling, pain, liquefaction, and pus, which in turn may lead to underarm pain in men. 3. Suppurative Sweatitis: It is a chronic suppurative inflammation of the parietal sweat glands, which occurs in the armpits. Due to the stimulation of inflammation, the initial stage is one or more small hard subcutaneous nodules, with the progress of time, pustules may appear on the surface of the nodules, and the symptoms of underarm sweating, pain and redness appear. Underarm pain in boys can also be seen in other diseases, it is recommended that patients go to the hospital in time, follow the doctor’s instructions for treatment, to avoid delaying the condition.